I use a Pi 2B with a home-made relais board to control my heating system in the house. Replaced my thermostats with ESP8266-based temperature sensors in each room, and the Pi decides when to run which circulation pump. It also records when the oil burner is firing, so I know how much heating oil I used at any time. A 2nd "central unit" Pi is running a MySql server for data storage and Web controls. That unit also has a infrared sensor to control Hue lights and similar things via IR remote. Finally, a few 1st-gen Pis act as a water alarm system, monitoring sensors on the basement floor (homegrown board measuring resistance between contacts). They have cheap USB cams and LED lights. On water detected, they alert me via text, take 20s video of the floor, and upload the video to dropbox so I can gauge how serious the issue is.

Being from Germany originally, I have liked always liked TMo in the US - friendly customer service, GSM technology (important if you travel overseas a lot), very good coverage (only in Puerto Rico I drew a blank so far) and the fact that they allow you to unlock the phone after a very short time (basically after you paid 3 bills or so). I have always been able to plug in my German pre-paid card and avoid overseas roaming charges. In addition, TMo is one of the few carriers to still offer an unlimited data plan, which came in really handy when Hurricane Irene took out my regular network for days.
But the selection of phones they offered in the past (before the iPhone - I don't really care about that) were clearly putting many folks off. They got the Razr at a time when people already dumped them on EBay, and only recently they got themselves a real winner with the Galaxy S/Vibrant. I always had a hard time defending our family plan with my kids with the "totally uncool" phones, and ended up buying unlocked phones on the free market a few times. I once found myself next to a T-Mo corporate woman on a flight and told her that. She was really surprised and recited the list of phones she thought were really great - almost the same selection that I knew to be the list of Phones Never To Be Caught With. It continued with the Android 1.5 phones that were offered forever, the Blackberries, and others which appeared to be selected for their total absence of any kind of must-have appeal.